There were two main projects to assess methyl bromide alternatives for the forest nursery industry. The first project evaluated reduced-rate alternative fumigants (Table 1) under a low-permeability plastic film (virtually impermeable film or VIF) in comparison to the traditional application rate of methyl bromide with chloropicrin under high density polyethylene (HDPE). The second project evaluated a different set of reduced-rate alternative fumigants under totally impermeable film (TIF) (Table 2). Biocontrol agents were tested in subplots within each of the fumigation treatments (Table 3). Both projects were conducted in Douglas-fir seedling plots and the efficacy of each treatment was measured on the basis of soilborne pathogen control (Pythium, Fusarium, and Cylindrocarpon species), weed control, seedling yield, and seedling quality.
The objectives of our studies were to:
- Compare efficacy of the traditional methyl bromide + chloropicrin fumigant treatment in reducing pathogen and weed populations to reduced-rate alternative fumigants.
- Compare fumigation efficacy on pathogen inoculum buried at 6 and 12 inch depths.
- Identify soilborne pathogen species found in forest nurseries of Oregon and Washington.
- Compare efficacy of methyl iodide under HDPE versus VIF.
- Quantify seedling morphology, yield, root infection, and economic impacts of reduced-rate alternative fumigant treatments.
Table 1. Fumigation treatments, rates, and plastic film for Project 1.
|Treatment||Application Rate||Plastic Film|
|Not fumigated (negative control)||None||HDPE|
|Methyl bromide + chloropicrin (positive control)||350 lbs/acre (67:33)||HDPE|
|Methyl iodide + chloropicrin||244 lbs/acre (50:50)||HDPE|
|Methyl iodide + chloropicrin||244 lbs/acre (50:50)||VIF|
|Metam sodium + chloropicrin||50 gal/acre + 122 lbs/acre||VIF|
|Dimethyl disulfide + chloropicrin||60 gal/acre (453 lbs + 120 lbs)||VIF|
- Compare efficacy of a reduced-rate methyl bromide + chloropicrin fumigant treatment to reduced-rate alternative fumigant treatments in reducing pathogen and weed populations.
- To determine if applied biocontrol agents augment control of soilborne pathogens.
Table 2. Fumigation treatments and rates for Project 2.
|Not fumigated (negative control)||None|
|Methyl bromide + chloropicrin||250 lbs/acre (50:50)|
|Pic-Chlor 60 (Chloropicrin + 1,3-D||285 lbs/acre (60:40)|
|Metam sodium + chloropicrin||27 gal/150 lbs/acre|
Table 3. Biocontrol treatments and agent for Project 2. Applied at label rates.
|Companion (Growth Products Ltd.)||Bacillus subtilis|
|Actinovate (Natural Industries Inc.)||Streptomyces lydicus|
|SoilGard (Certis USA LLC)||Gliocladium virens|
|RootShield (Bioworks Inc.)||Trichoderma harzianum|
In general, all reduced-rate alternative fumigant treatments were comparable to the methyl bromide treatment in reducing soilborne pathogen and weed populations. Fumigant efficacy was greater at 6 inches than at 12 inches of depth on buried inoculum and disease and weed control was similar regardless of the type of plastic film used (HDPE, TIF, or VIF). These reduced-rate treatments also resulted in similar Douglas-fir seedling yields and profit as the methyl bromide treatments (Table 4). Seedlings from plots without fumigation were of lower quality and yield than in fumigated plots. In addition, Pythium and Fusarium species were identified from forest nursery soils and seedlings, which will allow future research to more directly target pathogen species of interest. Biocontrol treatments were ineffective at controlling soilborne pathogens. Further results and information can be found in our two publications from Project 1. The publication for results from Project 2 is in progress.
Table 4. Douglas-fir seedling yield and profit
|Treatment||Seedling Yield/Acre||2010 Price/Seedling ($)||Gross Profit/Acre ($)||Fumigant Cost/Acre ($)||Net Profit/Acre ($)||Percent of MB Profit|
Acronyms for treatments: DMDS = dimethyl disulfide, HDPE = high density polyethylene, MB = methyl bromide, MI = methyl iodide, MS = metam soidum, NF = not fumigated, Pic = chloropicrin, VIF = virtually impermeable film.
Publications from Project 1.
Weiland, J. E., Leon, A. L., Edmonds, R. L., Littke, W. R, Browning, J. E., Davis, A., Beck, B. R., Miller, T. W., Cherry, M. L, and Rose, R. 2011. The effects of methyl bromide alternatives on soil and seedling pathogen populations, weeds, and seedling morphology in Oregon and Washington forest nurseries. Can. J. For. Res. 41: 1885-1896.
Weiland, J. E. 2011. Influence of isolation method on recovery of Pythium species from forest nursery soils in Oregon and Washington. Plant Disease. 95: 547-553.
Weiland, J. E., Littke, W. R., and Haase, D. L. 2013. Forest nurseries face critical choices with the loss of methyl bromide fumigation. Cal. Ag. 67: 153-161.
Weiland, J. E., Beck, B. R., and Davis, A. 2013. Pathogenicity and virulence of Pythium species obtained from forest nursery soils on Douglas-fir seedlings. Plant Disease. 97: 744-748.